The present invention concerns a device for venting a motor vehicle fuel tank.
For limiting air pollution, motor vehicle fuel tanks must eject as little fuel vapour as possible to the atmosphere. In order to be able to fill and then empty a fuel tank it is necessary to provide a venting device. Thus, during the filling phase, the air contained in the reservoir can escape, and during the emptying of the tank the air can re-enter it in order to replace the fuel consumed. The venting device also prevents overpressure or negative pressure in the reservoir when variations in temperature occur.
To limit the ejection of fuel vapour to the atmosphere, it is known that the venting device can be equipped with a canister which recovers the fuel escaping in the form of vapour during the vehicle running and parking phases. Thus the gas escaping from the tank is xe2x80x9cfilteredxe2x80x9d in order to recover the fuel and eject only air.
To prevent the ejection of fuel vapour into the atmosphere when the tank is filled, it is known that a nozzle with fuel vapour exhaust can be used. Such a nozzle is complex and its cost is high. Because of this such nozzles are uncommon or not in widespread use.
The technical problem at the basis of the present invention is to economically achieve a limitation to the ejection of fuel vapour into the atmosphere both during a tank filling phase and during running and parking phases.
The invention applies notably to vehicles consuming unleaded petrol. In this case, the tank filler pipe is provided at its entrance with a flap mounted so as to pivot. This prevents the introduction of fuel other than unleaded petrol.
The device proposed by the invention is a venting device intended for a motor vehicle tank having on the one hand a filler pipe provided with a flap mounted so as to pivot about a spindle, prestressed in the closed position and intended to be opened by the end of a filling nozzle, and on the other hand a pipe for venting the tank.
According to the invention, means are provided for closing off the vent pipe of the tank when it is being filled, being controlled by the pivoting of the flap about its spindle.
Making provision for acting on the venting device when the flap closing off the filling orifice is actuated makes it possible to treat solely the tank filling phase separately. The limitation of the ejection of fuel vapours into the atmosphere during refuelling is then dealt with directly by the venting system as described below with a few example embodiments or by means of a nozzle with fuel vapour exhaust.
In a preferential embodiment, the pivoting of the flap about its spindle mechanically drives a valve for effecting the opening and closing of the vent pipe.
Given that the rotation of the flap in the filling pipe does not exhibit a constant angular movement, provision is for example made for the valve to be a rotor valve and for the rotor of the valve and the spindle of the valve to be connected by elastic means, such as for example a spring. A movement less than the minimum movement of the flap to allow the passage of the end of a filling nozzle will be chosen for the rotor to ensure the complete movement of the rotor.
To limit the ejection of fuel vapours into the atmosphere, the vent pipe is advantageously connected to a fuel vapour filtration device. Thus the gases leaving the tank are filtered so as to recover the fuel, sending it for example to a fuel inlet device, and to eject into the atmosphere only relatively pure air.
A variant embodiment according to the invention provides for the vent pipe to connect the tank to a valve actuated by the flap, for the valve also to be connected to a fuel vapour filtration device and for a pipe to connect the tank to the filling pipe, close to the filling orifice.
In a preferential embodiment, the tank has two vent pipes each connected on the one hand to the tank and on the other hand to a valve controlled by the spindle of the flap situated in the filler pipe; the valve, in a first position corresponding to the closed position of the flap, connects a first vent pipe to a fuel vapour filtration device, the second vent pipe then being closed off by the valve, and the valve, in a second position corresponding to the open position of the flap, connects the second vent pipe to the fuel vapour filtration device, the first vent pipe then being closed off by the valve.
In this embodiment, the first pipe providing the venting is advantageously connected to the filler pipe when the flap is closed, by means of a non-return valve preventing any passage from the filler pipe to the vent pipes.
For this preferential embodiment, provision can be made for the valve to have a two-position rotor, two radial inlets disposed in the same plane with an angular offset corresponding to the magnitude of the rotation of the rotor and an outlet, and for the rotor, in each of its two positions, to block off an inlet, the other then being in communication with the outlet.
According to a first variant of this device, the rotor can have a longitudinal arm off-centre with respect to the rotation axis of the rotor and carrying a membrane substantially radial with respect to the movement of the rotor, blocking off an inlet in each of the two positions.
According to another variant embodiment, the rotor is in the form of a shaft with a cam which in a first position closes off one inlet and in the second position closes off a second inlet.
To limit the force to be exerted on the flap in order to open it and to be able to fill the tank, the flap has for example a hollow on its face intended to come into contact with a filling nozzle so that the contact between the nozzle and the flap takes place at a point distant from the pivot axis of the flap.
The present invention also concerns a tank, characterised in that it is equipped with a device as described above.
The invention, in broader terms, also concerns a tank having a filler pipe in which there is a flap prestressed in the closed position, characterised in that it has means for controlling a device for limiting the emission of polluting substances and/or a safety device, from the pivoting of the flap.